Synchronous motor starter



1941- SEEGER EI'AL 2,264,863

SYNCHRONOUS MOTOR STARTER Filed larch 27, 1939 L L5 L E w. s @uxfi 56m Patented Dec. 2, 1941 2,264,863 SYNCHRONOUS Moron sraa'rsa Edwin W. Seeger, Carroll Stansbury, and Victor S. Sywulka, Wauwatosa, Win, assignorl to Cutler-Hammer, Inc., Milwaukee, Wis.. a corporation of Delaware Application March 27, 1939, Serial No. 264,284

8 Claims.

This invention relates to the control of the direct current excitation of synchronous dynamoelectric machines which are started by the application of alternating current to their armature winding and when near synchronous speed have their field excited by direct current to thereafter pull into synchronism. The present invention is particularly applicable to the control of the field excitation of synchronous motors, as it not; only provides for the automatic excitation of the field winding when during the starting period the motor has accelerated to the proper speed, but it also provides for the temporary opening of the field excitation circuit if the motor after having been synchronized should fall out of step from any cause and for the reclosure of the field excitation circuit if the motor subsequently attains again the proper speed for closure of the field circuit.

An object of the invention is to provide auto- Another object is to provide an automatic controller of the aforementioned type which completes the closure of the field excitation circuit after initiation of such closure irrespective of a temporary rise of the armature current during synchronization 01' the motor.

Another object is to provide a relay for a controller of the aforementioned type which is responsive to the effective armature current to commutate the motor field circuit.

Another object is to provide time delay; means for controlling the field excitation of a synchronous motor in such a manner that the excitation control is not affected by transient currents incident to synchronization of themotor armature.

Other objects and advantages will hereinafter appear.

The accompanying drawing illustrates diagrammatically a motor control system which incorporates the invention.

The drawing shows the following: A three phase supply line L L L supplies an armature winding I of a synchronous motor with energy. The motor is provided with a direct current field winding I which may be supplied with energy from a direct current supply line L L The motor armature current is controlled by an electromagnetic main switch 2, having an energizing winding 2, normally open main contacts 2 2, 2 and normally open auxiliary contacts 2' and 2.

A current transformer I having a secondary winding 3' has its primary winding connected in series with the line L. A control relay 4 is provided with an energizing winding 4 and normally open contacts 4 and 4. A normally open push button switch 5 and a normally closed push button switch 5 provide for manual starting and stopping of the equipment. A timing relay 1 is provided with an energizing winding 1, and three armatures l 1 and I The armature l actuates a normally closed contact 1, the armature 1 a normally open contact I. and the armature l supports the insulated bridging member of normally open contacts 1'. An electromagnetic field switch 8 has an energizing winding 8, normally open contacts 8*, 3, 8 and normally closed contacts 8 and 8 A double throw relay 9 has a pivoted operating lever 9' which is arranged so that it may be rotated in opposite directions by armatures of magnets 9 and 9 respectively and so that it will remain in the position to which it has been moved when the respective magnet armature drops back by gravity. The magnet 9* may be energized by a magnetizing coil 9 tolift its armature for clockwise rotation of the lever 9 while a. coil 9 when energized is adapted to lift the armature of magnet 9 for counterclockwise rotation of the lever 9' while a coil 9 when energized exerts a downward pull on the armature of magnet 9 to prevent it from being liftedby the coil 9 The lever B is provided with an insulated conducting member adapted'to bridge stationary contacts 8 when the lever is in its extreme counterclockwise position and with similar insulating conducting members adapted to bridge stationary contacts Q and 9 respectively when the lever is in its extreme clockwise position. A condenser I0 is connected in series with a high resistor H to form a circuit in shunt with the winding l while a second low resistor 12 is connected between the common points of condenser l0 and resistor II and contacts 9 9 respectively. A resistor i3 is connected in series with contacts 8' across the field winding l In the following will be explained the connections and the operation of the system: Let it be assumed that the lines L L, L and the lines L", L are energized. To start the equipment the push button i is depressed, thereby establishing a.

circuit from line L over push button switches 5 and 6, coil 4', to line L. Thereupon relay 4 closes contacts 4 which shunt push button I so that the relay 4 remains energized when push button 5 is released. Should it be desired at any time to stop the equipment pushbutton 6 is momentarily The relay coil 8" energized when contacts I open by shuntdepressed, which opens the circuit of relay coil l and returns the relay to the oil position not to reclose until push button isagain depressed. When relay 4 is energized a second circuit is established from line L over contacts 4, 4, coil 2 to line L This energizes the main switch 2 and closes contacts 2, 2 and 2 thereby connecting the vmotor armature to the alternating current lines which starts the motor as an induction motor, the field winding i? being short circuited through the resistor l3 and contacts 8. A brief interval after closing of its main contacts the of contacts 2', but the armature 9 is prevented from lifting by the combined downward pull of coil 9= and gravity. A circuit is also established from line L" through contacts 2 9 9*..coil 1" to line L" which energizes relay I and opens contacts 1 and closes contacts I and 1'. and a circuit parallel to coil '1 is established through resistors H and I2 and condenser iii to line L". This charges condenser l0 rapidly to its full charge through the low resistor l2, only a small additional charge passing through the high resistor ll. Closure of contacts 'I short circuits the winding 9 If now the action of the system is repeated as aforedescribed.

It will be noted that for an closure of the field relay I determined by the time delay in the release of armature "l the winding 9 is short circuited to prevent the relay lever 9' from being actuated during. said interval I and thus disconnect the field switch. The purpose of this arrangement is to. preventtranslent peaks of current during the synchronization of the motor armature from causing the opening of the field switch. Furthermore a time delay is when the motor current on starting drops for closure oi the field circuit and the response oi the field switch.- This delay is provided by the armature current of the motor decreases as the motor accelerates, the pull of the winding 9'. which is now connected through the contacts 1' across the secondary winding 3' decreases to a point where the pull of winding 8 exceeds the pull of the winding 9' and the armature 9 moves the lever 9 counterclockwise to' open contacts 9*} and 9 and to close contacts 9'. Closure of contacts 9' prepares a circuit for energization of coil 8. Opening of contacts 9 and 8 opens the connection of coil 1 to line L but the mag- 1 netic flux in relay I is momentarily maintained and only decreases gradually as the condenser l0 discharges through coil 1', the decay of the flux being determined by the value of resistor I i. As the iiux gradually decreases the armature 1 drops and closes contacts 1, thereby completing an energizing circuit L over contacts l, l 2*, I, l ,.-coil 8', contacts 9' to line L. The relay 8 thereupon closes the contacts 8 to connect the field winding i across the lines L", L" and opens the shunt circuit through resistor It by opening of contacts 8'. also closes contacts 8'' which maintain ing the latter. Relay 8 also opens the contacts 8' thereby de-energizing coil 9? and it closes contacts 8 which short circuits coil 9.

After further decay of the flux of relay 1', the armature 1 drops. thereby opening contacts 1. After a further interval during which the motornormally synchronizes, the armature I drops and opens contacts 1' which re'inserts winding 9 into circuit with the transformer coil 3. If the current in the motor armature i should then exceed a given amount, as by failure to synchronize or by pulling out of step, the armature 9" again rotates the lever 9! clockwise, thereby deenergizing the iield relay 8, disconnecting the for the c0118 from line field circuit and reenergizing relay 1, whereupon winding. the combination of an the delay in the dropping of armature l and has the purpose to prevent the excitation of the motor on momentary transient dips in the starting current.

What we claim as new and desire to secure by Letters Patent is: v

1. In a controller for a synchronous dynamoelectric machine having an armature and a field winding, the combination of electromagnetic means for controlling the field winding in response to variations in the effective value of the armature current, and means responsive to the operation of said former means to modify the response of said former means for a'given time interval after establishment of energization of said field winding.

electric machine having an armature and a field winding, the combination of electromagnetic means responsive to the effective value of the armature current to effect energization of said field winding when said current is below a given value and to prevent energization thereof when said current exceeds said value, and means responsive to the operation of said former means to modify the response of said former means for a given time interval-after establishment of energization of said winding.

3. In a controller for a synchronous dynamoelectric machine having an armature and a field winding, the combination of an electromagnetic field switch for controlling said field winding. electromagnetic means for controlling said field switch in response to variations in the effective value-cf the armature current and means controlled by the operation of said field switch for modifying the current response oi said electromagnetic means for a given time interval after initial'operation of said field switch.

4; In a controller for a synchronous dynamoelectric machine having an armature and a field electromagnetic field switch for controlling said fleld windln8.-an electromagnetic timing relay, a double throw re lay-efiective in one position to energize said timing relay and in another position to energize said field switch, and provided with a first electromagnet adapted to be energized by the armature current of the motor for moving said relay to said one position and with a second electromagnet including electromagnetic biasing means for moving said relay to said other position and an energizing coil for said second electromagnet responsive to said armature. current to oppose said biasing means, said timing relay being provided with means to render said biasing means ineifective'when said field switch is energized and to modify response of said first electromaginterval after the energization of said net for a given time interval after initial energization of said field switch.

5. A relay for controlling the field excitation of velectromagnet including electromagnetic biasing means to 'eflect closure of said switch and an energizing winding responsive to said armature current and opposing said biasing means, means efiective during closure of said switch to render said biasing means ineflectlve to oppose said first electromagnet, and associated means to render said first electromagnet ineflective for a given time interval after initial closure of said switch.

6. A relay for controlling the field excitation of a synchronous motor having an armature, a field winding and an excitation circuit for the latter, comprising in combination with a plurality of alternately closed contacts, a first electromagnet adapted to be energized by the annature current of the motor to close certain of said contacts, a second electromagnet including electromagnetic biasing means to eflect closure of the other of said contacts and an energizing winding responsive to said armature current and opposing said biasing means, means effective during the closure of said other contacts to render said biasing means ineffective to oppose said first electromagnet, and means rendered efiective by the closure of certain of said contacts to render said first electromagnet ineffective and to maintain it inefifective for a given time interval after the opening of said last mentioned contacts.

7. A controller for a synchronous dynamoelectric machine having an armature and a field winding comprising, a main switch for energizing said armature and having an auxiliary contact, an electromagnetic field switch for energizing said field winding, a double throw relay having a pair of alternately closed switches, a first electromagnet adapted to be energized by the armature current or the motor to close one of said last mentioned switches, a second electromagnet including a coil to effect closure of the other of said last mentioned switches and a winding opposing the pull of said coil and responsive to said armature current, a timing relay having a control winding energized by closure or said one of said last mentioned switches and having a set of contacts operative with a time delay to energize said field switch upon movement of said double throw relay to open said one of said last mentioned switches and to close said other of said last mentioned switches and further having a, set of contacts for shunting said first electro magnet for a given time after the opening of said other of said last mentioned switches.

8. In a controller for a synchronous motor having an armature and a field winding, a main switch for connecting the armature to an alternating current source, a field switch for connecting said field winding to a direct current source, a timing relay and a double throw relay for controlling said field switch, said double throw relay having a pair of contacts adapted to afford energization of said timing relay in one of its positions and a second pair 01' contacts adapted to afford energization of said field switch in another position, a first coil responsive to the armature current of the motor for moving the double throw relay to said one position and an electromagnet having a coil arranged to be energized when said main switch is closed and said field switch is open for moving said double throw relay to said other position and another coil arranged to be energized by the armature current to oppose the action of the second mentioned coil, said timing relay having a pair of contacts cooperating with said second pair of contacts affording energization of said field switch upon deenergization of said timing relay with a time delay'and having another pair of contacts adapted to shunt said first coil of said double throw relay while the latter is in said one position and to maintain said shunt for a time interval after said double throw relay moves from said one to said other position.

EDWIN W. SEEGER. CARROLL STANSBURY. VICTOR S. SYWULKA. 

